Different services can be offered through a given physical wireless network. Those services might have totally different requirements. For example, remote control of manufacturing machines in hazardous environment might be associated with relatively small information payload, but the information needs to be received extremely reliably and with ultra-low latency. This type of service is associated with what is called Critical Machine-Type Communication (C-MTC). The same physical network might also support massive connectivity of devices such as a carpet cleanliness sensor in some rooms of a basement. Clearly, communication of the sensor information is not delay-sensitive and falls in the Massive MTC (M-MTC) family, not the C-MTC family. Still, both services could be offered through the same physical network using a set of physical resources. Clearly, one would like to ensure the high reliability of the C-MTC communication while being able to support M-MTC. An approach envisioned is to set aside and reserve some frequency resources, which would be exclusively available to the C-MTC service, to be able to fully control availability of resources for the C-MTC service. This approach is often called hard-slicing (of the frequency domain, in this example).
Doing hard-slicing nevertheless has some disadvantages. For example, it reduces the joint (combined C-MTC and other service types) achievable system capacity. Ultimately, what one would like to do is fully share resources and efficiently manage the service prioritization while guaranteeing some level of fairness, as may be described in a properly prepared service-level agreement. That way, if the system is under loaded by all service types, the resource sharing would fall back to hard-slicing, but when the system is overloaded, all system resources could be accessible by any service type. Access to all resources by all services is referred to herein as soft-slicing.
Doing soft-slicing is not straightforward. M-MTC communications can effectively use relatively long transmission intervals because of repetition to enhance coverage (i.e., multiple repetitions result in an effective transmission interval that is long as compared to a typical transmission interval when not using repetitions), while C-MTC communications can typically use very short transmission intervals because of the time criticality of the communications. Therefore, if M-MTC transmissions are scheduled over most of the frequency resources, they could actually make resources unavailable for an unacceptably long duration for some C-MTC sessions which need short duration but immediate resource access. Guaranteeing a certain level of quality of service for C-MTC traffic under such soft-slicing approach is then very difficult.
Accordingly, there is a need for methods for improved coexistence of delay-tolerant and delay-sensitive sessions.